🍳What CFM does this cooktop's hood need?

✓ Tested & verified Updated: Aug 8, 2026 How we calculate this

Range hood CFM calculator

Cooktop width (in)

Hood position

300 CFM

The room works out at 250 CFM — 300 is the nearest size actually sold.

Gas cooktops have a second rule: total burner BTU ÷ 100. A 60,000 BTU range wants 600 CFM regardless of its width — take whichever number is larger.

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What size range hood do you need?

100 CFM for every linear foot of cooktop against a wall, 150 for an island. A standard 30-inch range is 2.5 ft: 250 CFM on a wall, 375 in the middle of the room, so you buy the 300 or the 400.

An island hood needs half again as much because there are no walls to help. Against a wall the cabinetry and the back wall keep the plume rising into the hood; in the middle of a room the steam and grease spread sideways before they reach it, and the hood has to pull harder to capture the same cooking.

Gas ranges have a second rule that often wins: total burner output in BTU divided by 100. A 60,000 BTU professional range needs 600 CFM even though it is only 36 inches wide, because the hood is removing combustion products as well as steam.

Above 400 CFM, most codes require make-up air. A hood that large pulls enough air out of a modern airtight house to depressurise it, which can drag combustion gases back down a flue.

Range hoods are sized by what is underneath them, not by the size of the kitchen — which is why a big kitchen with a small hob needs less extraction than a galley with a professional range.

Cooktop	Against a wall	Island	Gas rule (BTU ÷ 100)
24 in	200 CFM	300 CFM	40,000 BTU → 400 CFM
30 in	250 CFM	375 CFM	50,000 BTU → 500 CFM
36 in	300 CFM	450 CFM	60,000 BTU → 600 CFM
48 in	400 CFM	600 CFM	80,000 BTU → 800 CFM
60 in	500 CFM	750 CFM	100,000 BTU → 1,000 CFM

Where the gas column is larger than the others — which it usually is on a serious range — that is the number to buy. And once any of these columns passes 400, budget for make-up air as part of the job rather than discovering it at inspection.

Frequently asked questions

How many CFM for a 30 inch range hood?

250 CFM by the linear-foot rule against a wall, so a 300 CFM hood. Over an island it becomes 375 and you buy the 400. If the range is gas and its burners total more than 25,000 BTU, use the BTU ÷ 100 rule instead and take whichever answer is bigger.

How wide should the hood be?

At least as wide as the cooktop, and three inches wider on each side is much better — six inches wider in total captures the plume that drifts off the front burners. Over an island, wider still is worth it, since there is nothing to stop sideways drift. The CFM calculation is based on the cooktop width, not the hood width.

What is make-up air and when do I need it?

Air deliberately brought into the house to replace what a large hood removes. Most codes require it above 400 CFM, because a modern airtight house cannot leak that fast: the hood depressurises it, and the easiest path for replacement air becomes down a water heater or furnace flue, bringing combustion gases with it. The provision is usually a powered damper interlocked with the hood.

Is a ducted hood better than a recirculating one?

For anything beyond light cooking, considerably. A recirculating hood filters grease and, with a charcoal filter, some odour, then returns the heat and all the moisture to the kitchen. A ducted hood removes them from the building. Where ducting is genuinely impossible, a recirculating hood plus a window is the compromise — but do not expect it to keep the kitchen dry.

How high above the cooktop should it be?

Usually 24 to 30 inches above an electric cooktop and 27 to 36 above gas, and always what the manufacturer specifies. Too high and the plume spreads before it is captured, so the CFM you sized for is not what you get. Too low and it is a burn hazard and a fire risk over gas.

Do I need more CFM for a wok or a grill?

Yes. High-output wok burners and indoor grills produce far more smoke and grease than the linear-foot rule anticipates, and they are exactly where the gas BTU rule earns its place. Add a size, and consider a hood that is deeper as well as more powerful — capture area matters as much as airflow.

How we calculate this

Hood airflow uses the industry convention of 100 CFM per linear foot of cooktop for a wall-mounted hood and 150 CFM per linear foot for an island hood, applied to the cooktop width entered. The result rounds up to the CFM ratings hoods are built in: 200, 300, 400, 500, 600, 700, 900 and 1,200. The alternative gas rule — total burner BTU per hour ÷ 100 — is stated on the page but not computed here, as burner totals vary by model; where the two rules disagree the larger figure governs. The 400 CFM make-up air threshold reflects common residential mechanical code requirements; the exact trigger varies by jurisdiction and should be confirmed locally.

Worked example

With Cooktop width (in) 30, Hood position Against a wall, this page works out 300 CFM. The room works out at 250 CFM — 300 is the nearest size actually sold.

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